Fluorine-substituted cyclohexylcyclohexene derivative

ABSTRACT

A compound represented by formula (I): ##STR1## wherein R represents a straight chain alkyl group having from 1 to 9 carbon atoms; ##STR2## represents ##STR3## represents a hydrogen atom or a fluorine atom; and ##STR4## has a trans (equatorial-equatorial) configuration, is disclosed. The compound of formula (I) exhibits a nematic phase in the vicinity of room temperature or in a temperature range higher than room temperature and has a small optical anisotropy and a positive dielectric anisotropy and is, therefore, useful in preparing a liquid crystal display cell excellent in viewing-angle characteristics.

FIELD OF THE INVENTION

This invention relates to a fluorine-substituted cyclohexylcyclohexenederivative useful as an electrooptical display material and anintermediate thereof and processes for preparing the same.

BACKGROUND OF THE INVENTION

Typical liquid crystal display cells heretofore developed include afield effect mode cell proposed by M. Schadt et al., Applied PhysicsLetters, Vol. 18, 127-128 (1971), a dynamic scattering mode cellproposed by G. H. Heilmeier et al., Proceeding of the I.E.E.E., Vol. 56,1162-1171 (1968), and a guest-host cell proposed by G. H. Heilmeier, etal., Applied Physics Letters, Vol. 13, 91 (1968) and D. L. White et al.,Journal of Appleid Physics, Vol. 45, 4718 (1974).

The most current of these liquid crystal display cells is a twistednematic code cell (TN cell), a kind of the field effect mode cells. Asreported by G. Bauer, Mol. Cryst. Liq. Cryst., Vol. 63, 45 (1981), theTN cell requires that a product of an optical anisotropy (Δn) of aliquid crystal material filled in the cell and a thickness (d)μm of aliquid crystal layer in the cell should be set at a certain specificvalue in order to prevent generation of an interference fringe on thecell surface which would impair the cell appearance. In the liquidcrystal cells for practical use, the abovedescribed product Δn.d is setat 0.5, 1.0, 1.6, or 2.2. In general, setting of the Δn.d value at 0.5brings about satisfactory viewing-angle characteristics, and setting at1.0, 1.6, or 2.2 brings about an improved contrast when seen from thefront. Therefore, it is usual to set the Δn.d value at 0.5 in caseswhere a liquid crystal display cell is demanded to be easy to see fromany direction, while, in cases where the cell is demanded to show acontrast from the front, the Δn.d value is set at 1.0, 1.6, or 2.2.

On the other hand, since the thickness of the liquid crystal layer inthe currently employed cells is usually selected from a limited range offrom 6 to 10 μm, setting of the Δn.d at 0.5 naturally needs a liquidcrystal material having a small Δn, while setting at 1.0 needs a liquidcrystal material having a large Δn. Hence, whether a liquid crystalmaterial should have a small Δn or a large Δn depends on the desireddisplay characteristics of a liquid crystal display cell.

Most of the practical liquid crystal materials are generally prepared bymixing several kinds of compounds exhibiting a nematic phase in thevicinity of room temperature and compounds exhibiting a nematic phase attemperatures higher than room temperature. Since these mixed liquidcrystals for practical use are required, in many cases, to exhibit anematic phase at least over the entire temperature range of from -30° C.to +65° C., compounds having a nematic phase in the vicinity of roomtemperature or in the temperature range higher than room temperature areneeded.

Further, the mixed liquid crystals in the TN cell should have positivedielectric anisotropy (Δε), thus needing those nematic liquid crystalcompounds whose value is positive.

SUMMARY OF THE INVENTION

One object of this invention is to provide a novel liquid crystalcompound exhibiting a nematic phase at around room temperature or in atemperature range higher than room temperature and having a small Δn anda positive Δε.

The present invention relates to a compound represented by formula (I):##STR5## wherein R represents a straight chain alkyl group having from 1to 9 carbon atoms; ##STR6## represents ##STR7## represents a hydrogenatom or a fluorine atom; and ##STR8## has a trans(equatorial-equatorial) configuration.

DETAILED DESCRIPTION OF THE INVENTION

The compound represented by formula (I) can be synthetized according tothe following reaction scheme A or B:

Scheme A:

Synthesis of Compounds (I) wherein ##STR9## wherein R and X are asdefined above.

Step 1

A compound of formula (II) is reacted with a Grignard reagent of formula(III) in an ether solvent, e.g., anhydrous diethyl ether or anhydroustetrahydrofuran (THF). After completion of the reaction, dilutehydrochloric acid is added dropwise to the reaction mixture to effecthydrolysis. The reaction product is extracted with an inert solvent,e.g., benzene or toluene, washed with water, and dried. The solvent isremoved from the extract by distillation under reduced pressure toobtain a compound of formula (IV).

Step 2

The compound of formula (IV) is dehydrated in an inert solvent, e.g.,benzene or toluene, in the presence of p-toluenesulfonic acid. Theproduct is washed with water, dried, and distilled under reducedpressure to remove the solvent. Recrystallization from ethanol yields acompound of formula (V).

Step 3

The compound of formula (V) is reduced in a mixed solvent of ethanol andn-hexane in the presence of Raney nickel as a catalyst. The reactionproduct is filtered to remove the catalyst, and the solvent is removedfrom the filtrate by distillation under reduced pressure.Recrystallization from ethanol gives a compound of formula (VI).

Step 4

The compound of formula (VI) is dissolved in an inert solvent, e.g.,benzene or toluene, and the solution is hydrolyzed with a strong acid,e.g., hydrochloric acid or sulfuric acid. The reaction mixture is washedwith water and dried. The solvent was removed by distillation underreduced pressure to obtain a compound of formula (VII).

Step 5

The compound of formula (VII) is reacted with an n-alkylmagnesiumbromide in an ether solvent, e.g., anhydrous diethyl ether or anhydrousTHF. After completion of the reaction, dilute hydrochloric acid is addeddropwise to the reaction mixture to effect hydrolysis. The reactionmixture is extracted with an inert solvent, e.g., benzene or toluene,washed with water, and dried. The solvent is removed from the extract bydistillation under reduced pressure to obtain a compound of formula(VIII).

Step 6

The compound of formula (VIII) is dehydrated in an inert solvent, e.g.,benzene or toluene, in the presence of p-toluenesulfonic acid. Thereaction product is washed with water and dried. The solvent is removedtherefrom by distillation under reduced pressure. Recrystallization fromethanol gives the entitled compound of formula (I-a).

Scheme B ##STR10## wherein R and X are as defined above. Step 1'

A compound of formula (IX) is reacted with a metallic magnesium powderin an ether solvent, e.g., anhydrous THF, at 20° to 30° C. for 1 to 2hours to prepare a compound of formula (III).

Step 2'

To a solution of the compound of formula (III) is added an anhydrous THFsolution of a compound of formula (X) at 5° to 20° C., followed byallowing the mixture to react at 10° to 30° C. for 30 minutes. Thereaction product is decomposed with a saturated aqueous solution ofammonium chloride to obtain a compound of formula (XI).

Step 3'

The compound of formula (XI) is refluxed in an inert water insolublesolvent, e.g., toluene, in the presence of an acidic catalyst, e.g.,p-toluenesulfonic acid, for 2 to 8 hours. After cooling the reactionmixture, the organic solvent layer is washed successively with asaturated aqueous solution of sodium carbonate and a saturated sodiumchloride aqueous solution and dried. The organic solvent is then removedby distillation. The resulting crude product is recrystallized from analcohol solvent, e.g., methanol, to obtain a compound of formula (XII).

Step 4'

The compound of formula (XII) is catalytically reduced in an alcoholsolvent, e.g., ethanol, in the presence of a hydrogenating catalyst,e.g., Raney nickel, under a hydrogen pressure of not higher than 3kg/cm² at room temperature for 6 to 20 hours to prepare a compound offormula (XIII).

Step 5'

The compound of formula (XIII) is reacted with an acidic aqueoussolution, e.g., dilute hydrochloric aicd, in an inert organic solvent,e.g., toluene, at reflux for 4 hours. The reaction mixture is cooled,and the organic solvent layer is washed with water and dried. Theorganic solvent is removed from the solution by distillation. Theresulting crude product is recrystallized from n-hexane to obtain acompound of formula (XIV).

Step 6'

A compound of formula (XV) is reacted with lithium in an ether solvent,e.g., anhydrous diethyl ether, at reflux for 2 to 8 hours to form alithium salt. To the reaction mixture is added a solution of thecompound of formula (XIV) in an ether solvent, e.g., anhydrous diethylether, at 0° to 15° C., and the mixture is allowed to react at 5° to 20°C. for 30 minutes. Water is added to the reaction mixture to performhydrolysis. The reaction product is extracted with toluene, and theextract is washed with water and dried. The solvent is removed from theextract by distillation to obtain a compound of formula (XVI).

Step 7'

The compound of formula (XVI) is dissolved in n-hexane, and the solutionis added to an acetonitrile solution of iodotrimethylsilane prepared byreacting chlorotrimethylsilane and sodium iodide in acetonitrile, andthe mixture is allowed to react at 5° to 10° C. for 30 minutes. To thereaction mixture is then added a base, e.g.,1,8-diaza-bicyclo(5,4,0)undecene-7 (DBU), followed by allowing to reactat 5° to 30° C. for 5 to 20 hours. Water is added to the reactionmixture, and the reaction product is extracted with toluene. The extractis washed successively with dilute hydrochloric acid, a saturated sodiumhydrogencarbonate aqueous solution, and a saturated sodium chlorideaqueous solution, followed by drying. The solvent is removed from theextract by distillation. The crude reaction product is refluxed in asolvent, e.g., toluene, in the presence of an acidic catalyst, e.g.,p-toluenesulfonic acid, for 1 to 8 hours to thereby isomerize thecyclohexane ring from a cis-configuration to a trans-configuration.Thus, there is obtained a mixture of a compound of formula (I-b) and acompound of formula (I-c) in good yield. After completion of thereaction, the toluene layer is washed successively with a saturatedsodium hydrogencarbonate aqueous solution and a saturated sodiumchloride aqueous solution, followed by drying. The toluene is removedfrom the extract by distillation. The crude reaction product is purifiedby silica gel column chromatography and then recrystallized fromethanol. The recrystallized mixture is separated into each component byliquid chromatography, and each of the thus separated compounds isrecrystallized from ethanol to obtain the compound of formula (I-b) andthe compound of formula (I-c).

The dicyclohexyl-4,4'-dione monoketal derivative represented by formula(II) is a novel compound.

The comound of formula (II) can be prepared according to the followingreaction scheme: ##STR11##

Step 1"

Biphenyl-4,4'-diol of formula (IX) is dissolved in an alcohol (e.g.,ethanol, isopropanol) and reduced in the presence of anhydrous sodiumcarbonate using 5 wt% palladium-on-carbon as a reducing catalyst under amedium pressure to prepaer dicyclohexyl-4,4'-diol of formula (X).

Step 2"

The compound of formula (X) obtained in Step 1" is dissolved in anon-polar organic solvent (e.g., toluene) and oxidized with an oxidizingagent (e.g., chromic acid) to prepare dicyclohexyl-4,4'-dione of formula(XI).

Step 3"

The compound of formula (XI) obtained in Step 2" is dissolved in anon-polar solvent (e.g., benzene, toluene) and subjected to dehydratingcondensation with a ketal agent (e.g., ethylene glycol,2-mercaptoethanol, 1,2-ethanedithiol) in the presence of an acidiccatalyst (e.g., potassium hydrogensulfate) to prepare a reaction mixturecontaining compounds of formulae (II), (XI), and (XII).

Step 4"

The reaction mixture obtained in Step 3" is reacted with sodiumhydrogensulfite in a two-phase system of water and toluene to form asodium hydrogensulfite salt of the compound of formula (XI), which isremoved by filtration. The organic layer separated from the filtrate isconcentrated to dryenss under reduced pressure, and the residue isdissolved in a polar organic solvent (e.g., ethyl acetate). The solutionis treated with a sodium hydrogensulfite aqueous solution having a highconcentration to form a salt of the compound of formula (II), followedby filtration. The collected crystals are treated with aqueous ammoniato form the compound of formula (II), extracted with toluene and washedwith water. The solvent is removed by distillation under reducedpressure. The resulting extract is purified, for example, byrecrystallization to prepare the compound of formula (II).

Transition temperatures of typical compounds of formula (I) are listedin Table 1 below.

                                      TABLE 1                                     __________________________________________________________________________     ##STR12##                                                                     No.Compound                                                                         R                                                                                   ##STR13##     X                                                                               Temperature (°C.)Transition               __________________________________________________________________________    1     n-C.sub.3 H.sub.7                                                                    ##STR14##    H                                                                                ##STR15##                                        2     n-C.sub.3 H.sub.7                                                                    ##STR16##    F                                                                                ##STR17##                                        3     n-C.sub.5 H.sub.11                                                                   ##STR18##    F                                                                                ##STR19##                                        4     n-C.sub.3 H.sub.7                                                                    ##STR20##    H                                                                                ##STR21##                                        5     n-C.sub.3 H.sub.7                                                                    ##STR22##    H                                                                                ##STR23##                                        6     n-C.sub.3 H.sub.7                                                                    ##STR24##    F                                                                                ##STR25##                                        7     n-C.sub.3 H.sub.7                                                                    ##STR26##    F                                                                                ##STR27##                                        __________________________________________________________________________     Note:                                                                         In Table 1, C represents a crystalline phase; N represents a nematic          phase; and I represents an isotropic liquid phase.                       

The compounds of formula (I) according to the present invention arenematic liquid crystal compounds having positive dielectric anisotropy.They can be used in dynamic scattering mode cells in the form of amixture with other nematic liquid crystal compounds having negativedielectric anisotropy, or in field effect mode cells in the form of amixture with other nematic liquid crystal compounds having positive ornegative dielectric anisotropy.

Typical examples of compounds which can preferably be mixed with thecompounds of the present invention to the above-described utility are4-substituted benzoic acid 4'-substituted phenyl ester, 4-substitutedcyclohexanecarboxylic acid 4'-substituted phenyl ester, 4-substitutedcyclohexanecarboxylic acid 4'-substituted biphenyl ester,4-(4-substituted cyclohexanecarbonyloxy)benzoic acid 4'-substitutedphenyl ester, 4-(4-substituted cyclohexyl)benzoic acid 4'-substitutedphenyl ester, 4-(4-substituted cyclohexyl)benzoic acid 4'-substitutedcyclohexyl ester, 4,4'-disubstituted biphenyl, 4-substitutedphenyl-4'-substituted-cyclohexane, substituted terphenyl, 4-substitutedbiphenyl-4'-substituted cyclohexane, 2-(4-substitutedphenyl)-5-substituted pyrimidine, etc.

Compound Nos. 2, 3, 6 and 7 having a formula (I) of the presentinvention shows a nematic phase at room temperature, and their physicalproperties are as shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                   Compound No.                                                                  2      3        6        7                                         ______________________________________                                        Δn (-) 0.0730   0.0634   0.0780 0.0750                                  Threshold Voltage (V)                                                                      1.87     1.68     1.95   1.91                                    Δε (-)                                                                       5.0      3.85     5.6    5.6                                     ______________________________________                                    

A mixture consisting of 40% by weight of Compound No. 1, 30% by weightof Compound No. 2, and 30% by weight of Compound No. 3 shows a nematicphase at a temperature between 0° C. and 66° C. and has a Δn of 0.0813,a threshold voltage of 2.25 V, and a Δε of 4.51.

A mixture consisting of 50% by weight of Compound No. 5 and 50% byweight of Compound No. 7 exhibits a nematic phase at a temperaturebetween 26° C. and 73° C. and has a Δn of 0.082 and a Δε of 4.6 asmeasured at room temperature in a supercooled state.

It can be understood from these results that the compounds of thepresent invention exhibit a nematic phase at around room temperature orat a temperature higher than room temperature and has a small Δn valueand a positive Δε value and are, therefore, suitable in preparingnematic liquid crystal display cells having excellent viewing-anglecharacteristics.

As described above, the compounds of formula (I) according to thepresent invention exhibit a nematic phase in the vicinity of roomtemperatures or in a temperature range higher than room temperature andhas an extremely small optical anisotropy Δn with a positive dielectricanistropy Δε. Therefore, these compounds are very useful as materialsfor preparing liquid crystal display cells excellent in viewing-anglecharacteristics.

The present invention is now illustrated in greater detail by way of thefollowing Examples, but it should be understood that the presentinvention is not deemed to be limited thereto. In these examples, allthe percents and ratios are given by weight unless otherwise indicated.

EXAMPLE 1

In 1 l of isopropanol was dissolved 100 g (0.54 mol) ofbiphenyl-4,4'-diol, and 5 g of anhydrous sodium carbonate and 5 g of 5%palladium-on-carbon were added to the solution. The mixture wassubjected to reduction reaction in an autoclave at 100° C. and at ahydrogen pressure of 5 kg/cm² for 25 to 30 hours. After completion ofthe reaction, the reaction mixture was filtered, and the isopropanol wasremoved from the filtrate by distillation under reduced pressure torecover a part of dicyclohexyl-4,4'-diol. The crystals obtained as afilter cake were dissolved in 500 ml of tetrahydrofuran while hot andfiltered. The tetrahydrofuran was removed from the filtrate bydistillation under reduced pressure to obtain dicyclohexyl-4,4'-diol.Both crystals were combined, suspended in 1 l of n-hexane while hot, andallowed to stand at 5° to 6° C. for 1 hour. The precipitated crystalswere collected by filtration and dried under reduced pressure to obtain93 g (0.47 mol) of a compound of formula: ##STR28## Melting Point:179°-181° C.

In 460 ml of toluene was dissolved 93 g (0.47 mol) of the compound, andto the solution was added dropwise a mixture which comprises 138 g (0.46mol) of sodium chromate dihydrate, 525 ml of water, 184 ml of sulfuricacid, and 55 ml of acetic acid, over a period of 2 hours whilemaintaining the solution at 40° C. or lower by stirring underwater-cooling. After the dropwise addition, the mixture was allowed tofurther react at that temperature for 2 hours, and an organic layer wasseparated from the reaction mixture. To the aqueous layer wa added 1 lof a saturated sodium chloride aqueous solution to effect salting out,followed by extracting twice with 300 ml portions of toluene. Theorganic layers were combined and washed with a saturated sodium chlorideaqueous solution until the washing became neutral. Then, the organiclayer was dried over anhydrous sodium sulfate and distilled underreduced pressure to remove the toluene. The residue was recrystallizedfrom a mixed solvent of 500 ml of n-hexane and 100 ml of ethyl acetateto obtain 68 g (0.35 mol) of a compound of formula: ##STR29## MeltingPoint: 117°-118° C.

To 340 ml of toluene were added 68 g (0.35 mol) of the resultingproduct, 26.2 g (0.42 mol) of ethylene glycol, and 130 mg of potassiumhydrogensulfate. The mixture was heat-refluxed in a reaction vesselequipped with a water separator while removing produced water out of thereaction system. After completion of the reaction, the reaction mixturewas allowed to cool to room temperature. As a result of gaschromatography, the reaction mixture was found to be a mixturecomprising compound of formulae: ##STR30## at a weight ratio of13:51:36.

To the reaction mixture was added a solution of 14.3 g (0.14 mol) ofsodium hydrogensulfite in 290 ml of water, followed by stirring for 30minutes. The thus precipitated sodium hydrogensulfite of a compound offormula: ##STR31## was separated by filtration. The filtrate wasseparated into an aqueous layer and an organic layer, and the organiclayer was distilled under reduced pressure to remove toluene. Theresidue was dissolved in 400 ml of ethyl acetate. To the solution wasagain added a solution of 70 g (0.67 mol) of sodium hydrogensulfite in250 ml of water, followed by stirring for 30 minutes. The thusprecipitated sodium hydrogensulfite of a compound of formula: ##STR32##was collected by filtration, washed two or three times with 200 mlportions of ethyl acetate, and poured into a large quantity of 10%aqueous ammonia, followed by stirring for 30 minutes. The reactionmixture was extracted twice with 200 ml portions of toluene, and theorganic layer was washed successively with a 5% sodium hydrogensulfiteaqueous solution and water and dried over anhydrous sodium sulfate. Thesolvent was removed by distillation under reduced pressure. The residuewas recrystallized from a mixed solvent of 500 ml of n-hexane and 100 mlof ethyl acetate to obtain 28.4 g of a compound of formula: ##STR33##Yield: 34% Melting Point: 109° C.

EXAMPLE 2

In 80 ml of anhydrous THF was dissolved 17.5 g (0.100 mol) ofp-bromofluorobenzene, and the solution was added dropwise to 2.67 g(0.110 gram atom) of a metallic magnesium powder at 30° to 40° C. whilestirring. The mixture was allowed to react at room temperature for anadditional period of 2 hours to form p-fluorophenylmagnesium bromide.

In 80 ml of anhydrous THF was dissolved 21.4 g (0.0899 mol) of acompound of Example 1 having formula: ##STR34## and the solution wasadded dropwise to the above-prepared Grignard reagent at 15° to 20° C.while stirring, and the mixture was allowed to further react at roomtemperature for 1 hour. After completion of the reaction, 100 ml of 2%dilute hydrochloric acid was slowly added dropwise to the reactionmixture while cooling. The reaction mixture was then extracted withtoluene, and the extract was washed with water until the washing becameneutral. Anhydrous sodium sulfate was added to the extract to dry it,followed by filtration. The solvent was removed from the filtrate bydistillation under reduced pressure to obtain a crude product offormula: ##STR35##

The crude product was dissolved in 150 ml of toluene, and 0.5 g ofp-toluenesulfonic acid monohydrate was added to the solution. Themixture was refluxed under stirring for 2 hours while removing theproduced water by decantation. The reaction mixture was cooled, and thetoluene layer was washed with water, dried over anhydrous sodiumsulfate, and distilled to remove the toluene. The resulting product wasrecrystallized from ethanol to obtain 18.5 g (0.0585 mol) of a compoundof formula: ##STR36##

The thus prepared compound was dissolved in a mixed solvent of 90 ml ofethanol and 90 ml of ethyl acetate and subjected to reduction using 2 gof Raney nickel as a catalyst under a hydrogen pressure of 3 kg/m².After the reaction, Raney nickel was separated by filtration, and thesolvent was removed from the filtrate by distillation to obtain a crudeproduct of formula: ##STR37##

The crude product was dissolved in 80 ml of toluene, and 50 ml of 25%sulfuric acid was added thereto, followed by stirring at 60° C. for 3hours. After cooling, the toluene layer was washed with water and driedover anhydrous sodium sulfate. The toluene was removed by distillation.Recrystallization of the resulting crude product yielded 9.74 g (0.0355mol) of a compound of the following formula (melting point: 92° C.):##STR38##

In 20 ml of anhydrous THF was dissolved 4.80 g (0.0390 mol) of n-propylbromide, and the solution was added dropwise to 1.04 g (0.0428 mol) of ametallic magnesium powder at 30° to 40° C. while stirring, followed byallowing the mixture to react at room temperature for 2 hours to preparea Grignard reagent. To the reaction mixture was added dropwise asolution of 9.74 g (0.0355 mol) of the above-prepared compound offormula: ##STR39## in 20 ml of anhydrous THF at 15° to 20° C. whilestirring, and the reaction was further continued at room temperature for1 hour. After completion of the reaction, 40 ml of 2% dilutehydrochloric acid was slowly added dropwise to the reaction mixturewhile cooling. The reaction mixture was extracted with toluene, and theextract was washed with water until the washing became neutral, anddried over anhydrous sodium sulfate. The solvent was removed therefromby distillation to obtain a crude product of formula: ##STR40##

The resulting crude product was dissolved in 100 ml of toluene, and 0.2g of p-toluenesulfonic acid monohydrate was added to the solution. Thesolution was refluxed under stirring while removing the produced waterby decantation. After effecting the dehydration reaction for 2 hours,the reaction mixture was cooled, and the toluene layer was washed withwater and dried over anhydrous sodium sulfate. The toluene was removedby distillation, and the resulting crude product was recrystallized fromethanol to obtain 6.25 g (0.0284 mol) of a compound of formula:##STR41## Yield: 31.6% Transition Temperature: 76° C. (C→N); 95° C. (N⃡I)

EXAMPLE 3

A compound of the following formula was obtained in the same manner asin Example 2, except for replacing the p-bromofluorobenzene with 19.3 g(0.100 mol) of 3,4-difluorobromobenzene. ##STR42## Yield: 20.6%Transition Temperature: 19° C. (C→N); 53° C. (N⃡I)

EXAMPLE 4

A compound of the following formula was obtained in the same manner asin Example 2, except for using 19.3 g (0.100 mol) of3,4-difluorobromobenzene in place of the p-bromofluorobenzene and usingn-pentyl bromide in place of the n-propyl bromide. ##STR43## Yield:18.7% Transition Temperature: -6° C. (C→N); 43° C. (N⃡I)

EXAMPLE 5

In 120 ml of anhydrous THF was dissolved 29.2 g (0.167 mol) ofp-bromofluorobenzene. The solution was added dropwise to 4.46 g (0.184gram atom) of a metallic magnesium powder at 20° to 30° C. whilestirring, and the reaction was further continued at room temperature(25° C.) for 2 hours to obtain a compound of formula: ##STR44##

In 40 ml of anhydrous THF was dissolved 20.0 g (0.128 mol) of a compoundof formula: ##STR45##

The solution was added dropwise to the above-prepared Grignard reagentat 10° to 15° C. while stirring, followed by allowing the mixture tofurther react at room temperature for 30 minutes. After the reaction,the reaction mixture was added to a saturated ammonium chloride aqueoussolution, and the mixture was extracted with toluene. The extract waswashed with water and dried, and the solvent was removed therefrom bydistillation to obtain 36.1 g of a crude product containing a compoundof formula: ##STR46##

The resulting crude product was dissolved in 250 ml of toluene, and 0.24g (0.0013 mol) of p-toluenesulfonic acid monohydrate was added thereto.The mixture was dehydrated by stirring at reflux for 2 hours, followedby cooling. The toluene layer was washed successively with a saturatedsodium hydrogencarbonate aqueous solution and a saturated sodiumchloride aqueous solution and dried. The toluene was removed bydistillation. Recrystallization of the product from methanol gave 17.0 g(0.073 mol) (yield: 56%) of a compound of formula: ##STR47##

This compound was dissolved in 170 ml of ethanol, and a catalytic amountof Raney nickel was added to the solution. The mixture was stirred atroom temperature at a pressure of 3.0 kg/m² or less to effecthydrogenation. After completion of the reaction, the catalyst wasremoved by filtration, and ethanol was removed from the filtrate bydistillation to obtain 17.2 g of a crude product containing a compoundof formula: ##STR48##

The resulting crude product was dissolved in 70 ml of toluene, and tothe solution was added 50 ml of 10% sulfuric acid, followed by stirringat reflux for 4 hours. After the reaction, the reaction mixture wascooled, and the toluene layer was washed with water, dried, anddistilled to removed the toluene. The residue was recrystallized fromn-hexane to obtain 13.1 g (0.0682 mol) (yield: 93%) of a compound offormula: ##STR49##

In 26 ml of anhydrous diethyl ether was dissolved 6.5 g (0.041 mol) of acompound of formula: ##STR50## and 0.57 g (0.083 gram atom) of lithiumwas added to the solution, followed by stirring at reflux for 5 hours.After completion of the reaction, the reaction mixture was cooled. Tothe reaction mixture was added dropwise 20 ml of an anhydrous diethylether solution containing 7.1 g (0.037 mol) of the above-preparedcompound of formula: ##STR51## at 8° to 12° C., and the reaction wascontinued at room temperature for an additional period of 30 minutes.The reaction mixture was poured into cold water, and the reactionproduct was extracted with toluene. The extract was washed with water,dried, and distilled to remove the solvent to obtain 11.9 g of a crudeproduct containing a compound of formula: ##STR52##

In 67 ml of acetonitrile was dissolved 17 g (0.110 mol) of sodiumiodide, and 12 g (0.110 mol) of chlorotrimethylsilane was added dropwisethereto. To the resulting solution was added dropwise 35 ml of ann-hexane solution containing the above-obtained crude product at 5° to10° C. while stirring, and the mixture was allowed to react at thattemperature for 30 minutes. To the reaction mixture was added dropwise20 g (0.130 mol) of DBU at 10° to 15° C., and the mixture was allowed tofurther react at room temperature (25° C.) for 19 hours while stirring.Water was added to the reaction mixture, and the reaction product wasextracted with toluene. The extract was washed successivly with dilutehydrochloric acid, a saturated aqueous solution of acid sodium sulfite,a saturated sodium hydrogencarbonate aqueous solution, and a saturatedsodium chloride aqueous solution, and dried. The solvent was removedfrom the extract by distillation to obtain a crude reaction product.

The crude product was dissolved in 50 ml of toluene, and 0.10 g (0.00053mol) of p-toluenesulfonic acid monohydrate was added thereto. Themixture was subjected to isomerization reaction by stirring at refluxfor 8 hours. After cooling, the toluene layer was washed successivelywith a saturated sodium hydrogencarbonate aqueous solution and asaturated sodium chloride aqueous solution and dried. Removal of thetoluene by distillation gave a crude reaction product. The crude productwas subjected to silica gel column chromatography and thenrecrystallized from ethanol to obtain 6.4 g (0.021 mol) (yield: 57%) ofa mixture consisting of two compounds having formulae shown below. Themixture exhibited a nematic phase at a temperature between 54° C. and96° C.

The mixture was subjected to high-performance liquid chromatography, andeach of the searated compounds was recrystallized from ethanol to obtainthe following compounds. ##STR53##

EXAMPLE 6

Two compounds of formulae shown below were obtained in the same manneras in Example 5, except for using 5.9 g (0.041 mol) of a compound offormula: ##STR54## in place of the compound of formula: ##STR55## asused in Example 5. ##STR56##

The 1:1 mixture of these two compounds showed a nematic phase at atemperature between 42° C. and 62° C.

EXAMPLE 7

Two compounds of formulae shown below were obtained in the same manneras in Example 5, except for using 7.1 g (0.041 mol) of a compound offormula: ##STR57## in place of the compound of formula: ##STR58## asused in Example 5. ##STR59##

The 1:1 mixture of these two compounds showed a nematic phase at atemperature between 42° C. and 91°.

EXAMPLE 8

A mixture of two compounds of formulae shown below was obtained in thesame manner as in Example 5, except for using 32.2 g (0.167 mol) of3,4-difluorobromobenzene in place of the p-bromofluorobenzene (totalyield: 36%).

The resulting mixture exhibited a nematic phase at a temperature between19° C. and 57° C. and had a Δn of 0.076, a Δε of 5.3, and a thresholdvoltage of 1.93 V as measured at room temperature.

The mixture was subjected to high performance liquid chromatography, andeach of the thus separated compounds was recrystallized from ethanol toobtain the following compounds. ##STR60## and with reference to specificembodiments thereof, it will be apparent to one skilled in the art thatvarious changes and modifications can be made therein without departingfrom the spirit and scope thereof.

The compound of formula (II) according to the present invention isuseful as a raw material for synthesizing compounds such as a compoundof formula (I-a) having cyclohexylcyclohexens ring or a compound havingdicyclohexane ring.

While the invention has been described in detail and with reference tospecific embodiment thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A compound represented by formula (I): ##STR61##wherein R represents a straight chain alkyl group having from 1 to 9carbon atoms; ##STR62## represents ##STR63## represents a hydrogen atomor a fluorine atom; and ##STR64## has a trans (equatorial-equatorial)configuration.
 2. A compound according to claim 1, wherein ##STR65## 3.A compound according to claim 2, wherein X is a hydrogen atom.
 4. Acompound according to claim 2, wherein X is a fluorine atom.
 5. Acompound according to claim 1, wherein ##STR66##
 6. A compound accordingto claim 5, wherein X is a hydrogen atom.
 7. A compound according toclaim 5, wherein X is a fluorine atom.
 8. A compound according to claim1, wherein ##STR67##
 9. A compound according to claim 8, wherein X is ahydrogen atom.
 10. A compound according to claim 8, wherein X is afluorine atom.
 11. A compound according to claim 3, wherein R is ann-propyl group.
 12. A compound according to claim 4, wherein R is ann-propyl group.
 13. A compound according to claim 4, wherein R is ann-pentyl group.
 14. A compound according to claim 6, wherein R is anethyl group.
 15. A compound according to claim 6, wherein R is ann-propyl group.
 16. A compound according to claim 6, wherein R is ann-butyl group.
 17. A compound according to claim 7, wherein R is ann-propyl group.
 18. A compound according to claim 9, wherein R is anethyl group.
 19. A compound according to claim 9, wherein R is ann-propyl group.
 20. A compound according to claim 9, wherein R is ann-butyl group.
 21. A compound according to claim 10, wherein R is ann-propyl group.